How to move a singleton raid1 drive from raid1 /dev/md2 to /dev/md1

How to move a singleton raid1 drive from raid1 /dev/md2 to /dev/md1

[Mitchell Laks]

Hi Software Raid Gurus!:

I have 

A1:~# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 hdb1[0] hdg1[1]
      244195904 blocks [2/2] [UU]

md1 : active raid1 hdc1[0]
      244195904 blocks [1/1] [U]

md2 : active raid1 hde1[0]
      244195904 blocks [1/1] [U]

Now I want to take /dev/hde1 and get rid of /dev/md2 and add /dev/hde1 
to /dev/md1.

First i made sure that /dev/md2 was unmounted. I then took it out 
of /etc/fstab.

Then I did:

A1:~# mdadm /dev/md2 -f /dev/hde1
mdadm: set /dev/hde1 faulty in /dev/md2

Then I tried:

A1:~# mdadm /dev/md2 -r /dev/hde1
mdadm: hot remove failed for /dev/hde1: Device or resource busy

So I didnt know what to do next. So I did

A1:~# mdadm -S /dev/md2

then I did

A1:~# mdadm /dev/md2 -r /dev/hde1
mdadm: cannot get array info for /dev/md2

obviously the wrong thing to do...

A1:~# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 hdb1[0] hdg1[1]
      244195904 blocks [2/2] [UU]

md1 : active raid1 hdc1[0]
      244195904 blocks [1/1] [U]

unused devices: <none>
A1:~#                                              



So I decided not to risk anything else, and I turn to you for help. I would 
like to take the device /dev/hde1 at this point and add it to /dev/md1 safely 
and then sync /dev/md1 to full raid1 status  ... Then I would like to adjust 
the /etc/mdadm.conf file ...

I guess I dont know the algorithm for ending a raid on a single 
drive/partition and then making it subservient to another drive in a raid1 
status.

Thank you all for your help!!!!

Mitchell Laks

Re: How to move a singleton raid1 drive from raid1 /dev/md2 to /dev/md1

[Neil Brown]

On Thursday April 7, mlaks@verizon.net wrote:
> Hi Software Raid Gurus!:
> 
> I have 
> 
> A1:~# cat /proc/mdstat
> Personalities : [raid1]
> md0 : active raid1 hdb1[0] hdg1[1]
>       244195904 blocks [2/2] [UU]
> 
> md1 : active raid1 hdc1[0]
>       244195904 blocks [1/1] [U]
> 
> md2 : active raid1 hde1[0]
>       244195904 blocks [1/1] [U]
> 
> Now I want to take /dev/hde1 and get rid of /dev/md2 and add /dev/hde1 
> to /dev/md1.

md1 is a 1-drive array.  You to make it a 2-drive array you need a
recent 2.6 kernel and a recent release of mdadm.  If you have these,
then

  mdadm -S /dev/md2  # shutdown md2 and release hde1
  mdadm /dev/md1 -a /dev/hde1 # add hde1 as a spare in md1
  mdadm -G -n2 /dev/md1 # grow md1 to have two devices.

If you don't have 2.6, then you will have to recreate md1 with
the desired number of components, which will require unmounting it.

   mdadm -S /dev/md2
   mdadm -S /dev/md1
   mdadm -C /dev/md1 -l1 -n2 /dev/hdc1 missing

   mdadm /dev/md1 -a /dev/hde1

NeilBrown

Re: How to move a singleton raid1 drive from raid1 /dev/md2 to /dev/md1

[Mitchell Laks]

Thanks you Neil!!

i am running debian sarge with 1.9 and kernel 2.6.8
I followed  your instructions 

  mdadm -S /dev/md2  # shutdown md2 and release hde1
  mdadm /dev/md1 -a /dev/hde1 # add hde1 as a spare in md1
  mdadm -G -n2 /dev/md1 # grow md1 to have two devices.

and now

wustl@A1:~$ cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 hdb1[0] hdg1[1]
      244195904 blocks [2/2] [UU]

md1 : active raid1 hde1[1] hdc1[0]
      244195904 blocks [2/2] [UU]


Yay!!!

Thank you very much.

Mitchell